xdiff

xdiff is a graphical utility for viewing the differences of a file and up to four revisions of that file. The text of the files is presented side by side with their differences aligned and highlighted in colour for easy identification. xdiff can be used to produce a merged version incorporating any combination of the differences. Simple editing features are also provided.

To use xdiff, enter the command: xdiff file1 file2

Additional information about xdiff can be found here.